1. Field of the Invention
This invention relates to apparatus for applying a continuous layer of a liquid onto the internal wall of a conduit, e.g. a pipeline.
2. Prior Art
In the pipelining of a viscous fluid, there is a pressure drop between the upstream and downstream portions of the flowing fluid due to interactions between the fluid and the internal pipeline wall. When the fluid is to be transported over long distances, a significant pressure drop can result in increased pumping costs and other economical disadvantages. It therefore becomes important to minimize interaction between the viscous liquid and the internal pipeline wall to reduce pressure drop in the system. One solution to this problem is to provide a thin layer of a drag reducing material to the internal pipeline wall which "lubricates" the wall and prevents interaction with the viscous liquid.
Several apparatus have been proposed for coating or maintaining a thin layer of a drag reducing material around the internal circumference of a pipeline. The following U.S. patents are representative:
U.S. Pat. No. 1,787,126 to Steinnes teaches a device for coating the interior surface of an empty conduit in which the device contains the coating material. The device must be externally positioned in the conduit prior to expelling the material onto the conduit with compressed air.
U.S. Pat. No. 2,353,951 to Wood et al teaches coating and densifying the interior of a metallic tube by spraying the surface with colloidal graphite and then passing rollers over the surface to force penetration of the graphite into the surface and densify the metal.
U.S. Pat. No. 2,792,807 to Cummings teaches a pipe coating machine which is power driven from a point external to the pipe. This machine is only practicable for use in short pipe segments.
U.S. Pat. No. 2,821,205 to Chilton et al teaches lubricating a pipeline containing flowing heavy oil by injecting a thin film of water around the inner pipeline wall through diagonal slots in the wall. The water film is removed from the flow, through similar slots, prior to passage through a pumping station to prevent emulsification of the oil and water.
U.S. Pat. No. 3,307,567 to Gogarty et al teaches lubricating a pipeline containing a flowing petroleum product by injecting water through microporous injectors spaced along the pipeline.
U.S. Pat. No. 3,447,507 to Poettmann teaches an apparatus for depositing a low viscosity fluid along the internal surface of a pipeline in which the flow of low viscosity fluid is responsive to the pressure exerted on the apparatus by the transport fluid.
U.S. Pat. No. 3,502,103 to Verschuur teaches a pipeline inlet device for forming an annular layer of water surrounding a viscous liquid which provides for co-axial, lateral flow of the liquids prior to their actual contact in the pipeline.
None of the above prior art systems provides an effective way for applying a uniform, continuous layer of a drag reducing material on the internal wall of a pipeline over long distances.